Patatin-like phospholipase domain-containing 3 and the pathogenesis and progression of pediatric nonalcoholic fatty liver disease

Lower gut microbiome diversity and higher abundance of proinflammatory genus Collinsella are associated with biopsy-proven nonalcoholic steatohepatitis

There is increasing evidence for the role of gut microbial composition in the pathogenesis of nonalcoholic fatty liver disease (NAFLD). Nonalcoholic steatohepatitis (NASH) is the most serious form of NAFLD where inflammation causes liver damage that can progress to cirrhosis. We have characterized the gut microbiome composition in UK patients with biopsy-proven NASH (n = 65) and compared it to that in healthy controls (n = 76). We report a 7% lower Shannon alpha diversity in NASH patients without cirrhosis (n = 40) compared to controls (p = 2.7x 10^-4) and a 14% drop in NASH patients with cirrhosis (n = 25, p = 5.0x 10^-4). Beta diversity (Unweighted UniFrac distance) was also significantly reduced in both NASH (p = 5.6x 10^-25) and NASH-cirrhosis (p = 8.1x 10^-7) groups. The genus most strongly associated with NASH in this study was Collinsella (0.29% abundance in controls, 3.45% in NASH without cirrhosis (False Discovery Rate (FDR) p = .008), and 4.38% in NASH with cirrhosis (FDR p = .02)). This genus, which has been linked previously to obesity and atherosclerosis, was also positively correlated with fasting levels of triglycerides (p = .01) and total cholesterol (p = 1.2x 10^-4) and negatively correlated with high-density lipoprotein cholesterol (p = 2.8x 10^-6) suggesting that some of the pathways present in this microbial genus may influence lipid metabolism in the host. In patients, we also found decreased abundance of some of the Ruminococcaceae which are known to produce high levels of short-chain fatty acids which can lower inflammation. This may thus contribute to pathology associated with NASH.

The Liver in Children With Metabolic Syndrome

Non-alcoholic fatty liver disease (NAFLD) is recognized as an emerging health risk in obese children and adolescents. NAFLD represents a wide spectrum of liver conditions, ranging from asymptomatic steatosis to steatohepatitis. The growing prevalence of fatty liver disease in children is associated with an increased risk of metabolic and cardiovascular complications. NAFLD is considered the hepatic manifestation of Metabolic Syndrome (MetS) and several lines of evidence have reported that children with NAFLD present one or more features of MetS. The pathogenetic mechanisms explaining the interrelationships between fatty liver disease and MetS are not clearly understood. Altough central obesity and insulin resistance seem to represent the core of the pathophysiology in both diseases, genetic susceptibility and enviromental triggers are emerging as crucial components promoting the development of NAFLD and MetS in children. In the present review we have identified and summarizied studies discussing current pathogenetic data of the association between NAFLD and MetS in children.

Gut microbiota, fatty liver disease, and hepatocellular carcinoma

Intestinal bacteria contribute to the pathogenesis of non-alcoholic fatty liver disease (NAFLD). Recently developed microbial profiling techniques are beginning to shed light on the nature of the changes in the gut microbiota that accompany NAFLD and non-alcoholic steatohepatitis (NASH). In this review, we summarize the role of gut microbiota in the development of NAFLD, NASH, and hepatocellular carcinoma (HCC). We highlight the mechanisms by which gut microbiota contribute to NAFLD/NASH, including through alterations in gut epithelial permeability, choline metabolism, endogenous alcohol production, release of inflammatory cytokines, regulation of hepatic Toll-like receptor (TLR), and bile acid metabolism. In addition, we analyze possible mechanisms for enhanced hepatic carcinogenesis, including alterations in bile acid metabolism, release of inflammatory cytokines, and expression of TLR-4. Finally, we describe therapeutic approaches for NAFLD/NASH and preventive strategies for HCC involving modulation of the intestinal microbiota or affected host pathways. Although recent studies have provided useful information, large-scale prospective studies are required to better characterize the intestinal microbiota and metabolome, in order to demonstrate a causative role for changes in the gut microbiota in the etiology of NAFLD/NASH, to identify new therapeutic strategies for NAFLD/NASH, and to develop more effective methods of preventing HCC.

Pathophysiology of Nonalcoholic Fatty Liver Disease/Nonalcoholic Steatohepatitis

Nonalcoholic fatty liver disease (NAFLD) encompasses a spectrum of liver disorders ranging from hepatic steatosis to nonalcoholic steatohepatitis (NASH) and ultimately may lead to cirrhosis. Hepatic steatosis or fatty liver is defined as increased accumulation of lipids in hepatocytes and results from increased production or reduced clearance of hepatic triglycerides or fatty acids. Fatty liver can progress to NASH in a significant proportion of subjects. NASH is a necroinflammatory liver disease governed by multiple pathways that are not completely elucidated. This review describes the main mechanisms that have been reported to contribute to the pathophysiology of NAFLD and NASH.

Adiposity amplifies the genetic risk of fatty liver disease conferred by multiple loci

Complex traits arise from the interplay between genetic and environmental factors. The actions of these factors usually appear to be additive, and few compelling examples of gene-environment synergy have been documented. Here we show that adiposity significantly amplifies the effect of three sequence variants (PNPLA3-I148M, TM6SF2-E167K and GCKR-P446L) associated with nonalcoholic fatty liver disease (NAFLD). Synergy between adiposity and genotype promoted the full spectrum of NAFLD, from steatosis to hepatic inflammation to cirrhosis. We found no evidence of strong interactions between adiposity and sequence variants influencing other adiposity-associated traits. These results indicate that adiposity may augment genetic risk of NAFLD at multiple loci through at least three different metabolic mechanisms.

Epidemiology of NAFLD and Type 2 Diabetes: Health Disparities Among Persons of Hispanic Origin

Non-alcoholic fatty liver disease (NAFLD) is the most common chronic liver condition in the USA and worldwide and affects Hispanics disproportionally. In this review, we aim to document and contrast the epidemiology of NAFLD and type 2 diabetes, provide a framework to study health disparities in NAFLD in Hispanic populations, and identify points of action within the health care system to tackle these health disparities. NAFLD shares many common risk factors with type 2 diabetes, specially obesity and insulin resistance, but shows different prevalence patterns by ethnicity: while Hispanics are disproportionately affected by both NAFLD and type 2 diabetes, non-Hispanic black populations have a low prevalence of NAFLD. The current literature suggests a strong role of polymorphisms in the PNPLA3 gene and potential interactions with environmental factors in the pathogenesis of NAFLD. However, given potential interactions and the shared risk factors with type 2 diabetes, a health disparity approach that acknowledges upstream determinants is needed. Solutions to these determinants can also be found in the health system. The role of interventions that have shown efficacy in type 2 diabetes, like community health workers, may be implemented to prevent and control NAFLD.

Role of the Gut Microbiome in Nonalcoholic Fatty Liver Disease

The incidence of nonalcoholic fatty liver disease (NAFLD) continues to increase with prevalence estimates ranging from 17%-33%, making it is the most common cause of chronic liver disease in North America. Its importance is due to not only its prevalence but also its association with increased cardiovascular morbidity and progression to cirrhosis in a subset of patients. NAFLD encompasses a pathologic spectrum of disease, from relatively benign accumulation of lipid (steatosis) to progressive nonalcoholic steatohepatitis associated with inflammation, fibrosis, and necrosis. Nonalcoholic steatohepatitis remains an important phenotypic state because this subgroup of patients is deemed at high risk for developing cirrhosis and progressing to liver failure requiring transplantation or to death. Gut microbiota has recently been identified as regulators of energy homeostasis and fat deposition, thereby implicating them in the development of obesity and associated metabolic diseases. The growing evidence that alteration in gut microbiota (dysbiosis) may affect liver pathology may allow for a better understanding of its role in the pathogenesis of NAFLD, help to identify patients at risk of progression, and expose a microbial target for prevention and therapeutic intervention. In this review, we discuss the growing evidence that highlights the relationship between gut microbiota and its association with NAFLD.

Association between patain-like phospholipase domain-containing protein 3 rs738409(C>G) single nucleotide polymorphism and etiology of liver cirrhosis in a Chinese Han population

AIM: To determine whether patain-like phospholipase domain-containing protein 3 (PNPLA3) rs738409 single nucleotide polymorphism (SNP) affects the severity of hepatic damage, susceptibility and prognosis of liver cirrhosis with various liver diseases.

METHODS: We enrolled 224 Chinese Han patients diagnosed with liver cirrhosis, of whom 88 had hepatitis B virus (HBV)-related cirrhosis, 83 had alcoholic liver cirrhosis and 53 had hepatitis C virus (HCV)-related cirrhosis. Two hundred healthy volunteers were enrolled as a control group. TaqMan genotyping assay was used to investigate the association of PNPLA3 SNPs (rs738409) with the risk of liver cirrhosis.

RESULTS: The G allele of the PNPLA3 I148M variant was significantly different between alcoholic liver cirrhosis and the control (OR = 1.902, P < 0.001), and was associated with HBV-related liver cirrhosis (OR = 1.452, P = 0.047). There was no significant association between PNPLA3 rs738409 genotype and HCV-related cirrhosis (P = 0.056). There was no correlation between PNPLA3 rs738409 genotype and liver cirrhosis with hepatocellular carcinoma (P = 0.965).

CONCLUSION: PNPLA3 rs738409 C > G is associated with alcoholic liver cirrhosis and HBV-related liver cirrhosis in a Chinese Han population.

Hepatic patatin-like phospholipase domain-containing protein 3 sequence, single nucleotide polymorphism presence, protein confirmation, and responsiveness to energy balance in dairy cows

Patatin-like phospholipase domain-containing protein 3 (PNPLA3), commonly known as adiponutrin, is part of a novel subfamily of triglyceride lipase enzymes with potential effects on triglyceride metabolism in adipose and hepatic tissues. The predicted bovine PNPLA3 sequence has been identified, but expression of the gene had not been examined. The objectives of this study were to confirm the predicted bovine PNPLA3 gene sequence, determine expression of the bovine PNPLA3 gene in response to whole-animal energy balance, identify single nucleotide polymorphisms present in dairy cows, and verify the presence of the protein in the liver. Using liver biopsy samples collected from cows at +28d relative to calving (DRTC), RNA was isolated and used to generate a cDNA template for amplification of the entire predicted coding sequence of PNPLA3 via PCR. To determine if energy balance alters the expression of PNPLA3, RNA was isolated and mRNA expression quantified in liver samples from mid-lactation cows after a 5-d ad libitum period (n=5) and after a subsequent 5-d 50% feed restriction period (n=5), and in samples collected from cows at -14, +1, +14, and +28 DRTC (n=16). The presence of PNPLA3 protein was detected by Western blot in liver protein samples collected at +28 DRTC. Expression of hepatic PNPLA3 was decreased after a period of feed restriction (8.14 vs. 1.08±2.17 arbitrary units, ad libitum vs. fasted). Expression of PNPLA3 mRNA was decreased at +1 and +14 DRTC compared with -14 DRTC (23.35, 7.28, 10.17, and 14.5±4.9 arbitrary units, -14, +1, +14, and +28 DRTC, respectively). The presence of PNPLA3 protein was detected as a 55-kDa band in hepatic protein isolations from liver tissue collected at +28 DRTC. These data confirm the presence and sequence of the bovine hepatic PNPLA3 gene and single nucleotide polymorphisms. Furthermore, these data indicate responsiveness of bovine hepatic PNPLA3 to energy balance.

Chemical modulation of glycerolipid signaling and metabolic pathways

Thirty years ago, glycerolipids captured the attention of biochemical researchers as novel cellular signaling entities. We now recognize that these biomolecules occupy signaling nodes critical to a number of physiological and pathological processes. Thus, glycerolipid-metabolizing enzymes present attractive targets for new therapies. A number of fields-ranging from neuroscience and cancer to diabetes and obesity-have elucidated the signaling properties of glycerolipids. The biochemical literature teems with newly emerging small molecule inhibitors capable of manipulating glycerolipid metabolism and signaling. This ever-expanding pool of chemical modulators appears daunting to those interested in exploiting glycerolipid-signaling pathways in their model system of choice. This review distills the current body of literature surrounding glycerolipid metabolism into a more approachable format, facilitating the application of small molecule inhibitors to novel systems. This article is part of a Special Issue entitled Tools to study lipid functions.

Increased activin bioavailability enhances hepatic insulin sensitivity while inducing hepatic steatosis in male mice

The development of insulin resistance is tightly linked to fatty liver disease and is considered a major health concern worldwide, although their mechanistic relationship remains controversial. Activin has emerging roles in nutrient homeostasis, but its metabolic effects on hepatocytes remain unknown. In this study, we investigated the effects of increased endogenous activin bioactivity on hepatic nutrient homeostasis by creating mice with inactivating mutations that deplete the circulating activin antagonists follistatin-like-3 (FSTL3) or the follistatin 315 isoform (FST315; FST288-only mice). We investigated liver histology and lipid content, hepatic insulin sensitivity, and metabolic gene expression including the HepG2 cell and primary hepatocyte response to activin treatment. Both FSTL3-knockout and FST288-only mice had extensive hepatic steatosis and elevated hepatic triglyceride content. Unexpectedly, insulin signaling, as assessed by phospho-Akt (a.k.a. protein kinase B), was enhanced in both mouse models. Pretreatment of HepG2 cells with activin A increased their response to subsequent insulin challenge. Gene expression analysis suggests that increased lipid uptake, enhanced de novo lipid synthesis, decreased lipolysis, and/or enhanced glucose uptake contribute to increased hepatic triglyceride content in these models. However, activin treatment recapitulated only some of these gene changes, suggesting that increased activin bioactivity may be only partially responsible for this phenotype. Nevertheless, our results indicate that activin enhances hepatocyte insulin response, which ultimately leads to hepatic steatosis despite the increased insulin sensitivity. Thus, regulation of activin bioactivity is critical for maintaining normal liver lipid homeostasis and response to insulin, whereas activin agonists may be useful for increasing liver insulin sensitivity.

Paradoxical lower serum triglyceride levels and higher type 2 diabetes mellitus susceptibility in obese individuals with the PNPLA3 148M variant

Background

Obesity is highly associated with elevated serum triglycerides, hepatic steatosis and type 2 diabetes (T2D). The I148M (rs738409) genetic variant of patatin-like phospholipase domain-containing 3 gene (PNPLA3) is known to modulate hepatic triglyceride accumulation, leading to steatosis. No association between PNPLA3 I148M genotype and T2D in Europeans has been reported. Aim of this study is to examine the relationship between PNPLA3 I148M genotypes and serum triglycerides, insulin resistance and T2D susceptibility by testing a gene-environment interaction model with severe obesity.

Methods and Findings

PNPLA3 I148M was genotyped in a large obese cohort, the SOS study (n = 3,473) and in the Go-DARTS (n = 15,448), a T2D case-control study. Metabolic parameters were examined across the PNPLA3 I148M genotypes in participants of the SOS study at baseline and at 2- and 10-year follow up after bariatric surgery or conventional therapy. The associations with metabolic parameters were validated in the Go-DARTS study. Serum triglycerides were found to be lower in the PNPLA3 148M carriers from the SOS study at baseline and from the Go-DARTS T2D cohort. An increased risk for T2D conferred by the 148M allele was found in the SOS study (O.R. 1.09, 95% C.I. 1.01-1.39, P = 0.040) and in severely obese individuals in the Go-DARTS study (O.R. 1.37, 95% C.I. 1.13-1.66, P = 0.001). The 148M allele was no longer associated with insulin resistance or T2D after bariatric surgery in the SOS study and no association with the 148M allele was observed in the less obese (BMI<35) individuals in the Go-DARTS study (P for interaction  = 0.002). This provides evidence for the obesity interaction with I48M allele and T2D risk in a large-scale cross-sectional and a prospective interventional study.

Conclusions

Severely obese individuals carrying the PNPLA3 148M allele have lower serum triglyceride levels, are more insulin resistant and more susceptible to T2D. This study supports the hypothesis that obesity-driven hepatic lipid accumulation may contribute to T2D susceptibility.

Variant in the glucokinase regulatory protein (GCKR) gene is associated with fatty liver in obese children and adolescents

Recently, the single nucleotide polymorphism (SNP) identified as rs1260326, in the glucokinase regulatory protein (GCKR), was associated with hypertriglyceridemia in adults. Because accumulation of triglycerides in hepatocytes represents the hallmark of steatosis, we aimed to investigate whether this variant might be associated with fatty liver (hepatic fat content, HFF%). Moreover, because recently rs738409 in the PNPLA3 and rs2854116 in the APOC3 were associated with fatty liver, we explored how the GCKR SNP and these two variants jointly influence hepatosteatosis. We studied 455 obese children and adolescents (181 Caucasians, 139 African Americans, and 135 Hispanics). All underwent an oral glucose tolerance test and fasting lipoprotein subclasses measurement by proton nuclear magnetic resonance. A subset of 142 children underwent a fast gradient magnetic resonance imaging to measure the HFF%. The rs1260326 was associated with elevated triglycerides (Caucasians P = 0.00014; African Americans P = 0.00417), large very low-density lipoprotein (VLDL) (Caucasians P = 0.001; African Americans, P = 0.03), and with fatty liver (Caucasians P = 0.034; African Americans P = 0.00002; and Hispanics P = 0.016). The PNPLA3, but not the APOC3 rs2854116 SNP, was associated with fatty liver but not with triglyceride levels. There was a joint effect between the PNPLA3 and GCKR SNPs, explaining 32% of HFF% variance in Caucasians (P = 0.00161), 39.0% in African Americans (P = 0.00000496), and 15% in Hispanics (P = 0.00342).

CONCLUSION

The rs1260326 in GCKR is associated with hepatic fat accumulation along with large VLDL and triglyceride levels. GCKR and PNPLA3 act together to convey susceptibility to fatty liver in obese youths.

The association of PNPLA3 variants with liver enzymes in childhood obesity is driven by the interaction with abdominal fat

Background and Aims

A polymorphism in adiponutrin/patatin-like phospholipase-3 gene (PNPLA3), rs738409 C->G, encoding for the I148M variant, is the strongest genetic determinant of liver fat and ALT levels in adulthood and childhood obesity. Aims of this study were i) to analyse in a large group of obese children the role of the interaction of not-genetic factors such as BMI, waist circumference (W/Hr) and insulin resistance (HOMA-IR) in exposing the association between the I148M polymorphism and ALT levels and ii) to stratify the individual risk of these children to have liver injury on the basis of this gene-environment interaction.

Methods

1048 Italian obese children were investigated. Anthropometric, clinical and metabolic data were collected and the PNPLA3 I148M variant genotyped.

Results

Children carrying the 148M allele showed higher ALT and AST levels (p = 0.000006 and p = 0.0002, respectively). Relationships between BMI-SDS, HOMA-IR and W/Hr with ALT were analysed in function of the different PNPLA3 genotypes. Children 148M homozygous showed a stronger correlation between ALT and W/Hr than those carrying the other genotypes (p: 0.0045) and, therefore, 148M homozygotes with high extent of abdominal fat (W/Hr above 0.62) had the highest OR (4.9, 95% C. I. 3.2–7.8, p = 0.00001) to develop pathologic ALT.

Conclusions

We have i) showed for the first time that the magnitude of the association of PNPLA3 with liver enzymes is driven by the size of abdominal fat and ii) stratified the individual risk to develop liver damage on the basis of the interaction between the PNPLA3 genotype and abdominal fat.

The PNPLA3 rs738409 148M/M genotype is a risk factor for liver cancer in alcoholic cirrhosis but shows no or weak association in hepatitis C cirrhosis

BACKGROUND

An isoleucine>methionine mutation at position 148 in the PNPLA3 gene (p.I148M, rs738409) has recently been identified as a susceptibility factor for liver damage in steatohepatitis. Here, we studied whether the PNPLA3 rs738409 polymorphism also affects predisposition to hepatocellular carcinoma (HCC).

METHODS

We compared distributions of PNPLA3 genotypes in 80 and 81 Caucasian patients with alcoholic and hepatitis C virus (HCV)-associated HCC to 80 and 81 age- and sex-matched patients with alcohol-related and HCV-related cirrhosis without HCC, respectively. PNPLA3 genotypes in 190 healthy individuals from the same population served as reference. Potential confounders obesity, diabetes, HCV genotype and HBV co-infection were controlled by univariate and multivariate logistic regression with forward variable selection.

RESULTS

PNPLA3 genotypes were in Hardy-Weinberg equilibrium for all study groups. The frequency of the 148M allele was significantly (p<0.001) increased in alcoholic cirrhosis with (53.7%) and without HCC (36.2%) but was not different between healthy controls (22.9%) and patients with cirrhosis (25.3%; p = 0.545) and HCC (30.2%; p = 0.071) due to hepatitis C. HCC risk was highest in 148M/M homozygous patients with alcoholic liver disease (odds ratio (OR) 16.8 versus healthy controls; 95% confidence interval (CI) 6.68-42.43, p<0.001). Finally, multivariate regression confirmed 148M/M homozygosity (OR 2.8; 95%-CI: 1.24-6.42; p = 0.013) as HCC risk factor in alcoholic cirrhosis. In HCV-related cirrhosis only HCV genotype 1 was confirmed as a HCC risk factor (OR 4.2; 95%-CI: 1.50-11.52; p = 0.006).

CONCLUSION

The PNPLA3 148M variant is a prominent risk factor for HCC in patients with alcoholic cirrhosis, while its effects are negligible in patients with cirrhosis due to HCV. This polymorphism provides an useful tool to identify individuals with particularly high HCC risk in patients with alcoholic liver disease that should be taken into account in future HCC prevention studies.

Genetic variants in candidate genes influencing NAFLD progression

Nonalcoholic fatty liver disease (NAFLD) is a metabolic disorder including simple steatosis and nonalcoholic steatohepatitis (NASH). Advanced stages of NASH result ultimately in fibrosis, cirrhosis, and hepatocarcinoma. A diagnosis of NASH entails an increased risk of both liver-related and cardiovascular mortality as worsening of the metabolic syndrome. Because of its escalation, many investigations have been performed to elucidate the pathophysiologic origins of the disease progression. Human epidemiologic studies describing polymorphisms in a number of genes involved in metabolic dysfunctions have contributed to clarify the causes leading to the disease evolution. In this review, we attempt to outline critically the most recently identified genetic variants in NAFLD patients to identify possible risk factors promoting the progression of the disease. The evaluation of altered genotypes together with other clinical variables may facilitate the clinical management of these patients.

PNPLA3 rs738409C/G polymorphism in cirrhosis: relationship with the aetiology of liver disease and hepatocellular carcinoma occurrence

BACKGROUND AND AIM

The PNPLA3 rs738409 C>G polymorphism has been found to be strongly associated with non-alcoholic fatty liver disease and with alcoholic liver disease. Whether the PNPLA3 rs738409 polymorphism could be a risk factor for the development of hepatocellular carcinoma (HCC) in cirrhosis patients is unknown.

METHODS

This study included 483 (344 males) consecutive Italian patients of Caucasian ethnicity affected by cirrhosis, of whom 279 had undergone transplantation for end-stage liver disease while 204 had been referred to our liver and transplant unit for the diagnosis of cirrhosis. The aetiologies were hepatitis C virus=209, hepatitis B virus=76, alcohol=166, metabolic=32. Ile148Met rs738409 transversion was genotyped using an restriction fragment length polymorphism-based assay.

RESULTS

The genotype frequencies of the rs738409 polymorphism were distributed differently in patients with cirrhosis C/C=168, C/G=220, G/G=95 vs controls C/C=218, C/G=175, G/G=35 (P<0.0001). Among cirrhotics, the G allele was over-represented in alcoholic/metabolic (0.505) vs viral (0.368, P<0.001) liver disease. Patients with cirrhosis complicated by HCC were more likely to be G/G homozygotes (38/141) than the remaining patients (57/342, P<0.02). At multivariate analysis, the PNPLA3 rs738409 polymorphism was confirmed to be an independent predictor of HCC occurrence (odds ratio 1.76, 95% confidence interval 1.06-2.92, P<0.05). HCC rates increased from 13/116 (11.2%; female C/(*) carriers), to 97/295 (32.9%; male C/(*) carriers and female G/G homozygotes), to 31/72 (43.1%; male G/G homozygotes) (P<0.0001).

CONCLUSIONS

The PNPLA3 rs738409 C>G polymorphism is associated with cirrhosis. In synergy with gender, this polymorphism is a strong predictor of HCC occurrence among patients with cirrhosis.

Prepubertal gynecomastia in two monozygotic twins with Peutz-Jeghers syndrome: two years' treatment with anastrozole and genetic study

Peutz-Jeghers syndrome (PJS) is a rare autosomal dominant disorder characterized by multiple gastrointestinal hamartomatous polyps, mucocutaneous pigmentation and increased predisposition to neoplasms. Endocrine manifestations in PJS include gynecomastia and advanced bone age due to estrogen production by large-cell calcifying Sertoli cell tumors (LSCT). We present two 9-year-old male monozygotic twins, with PJS, bilateral progressive prepubertal gynecomastia and testicular bilateral multifocal calcifications, suggesting a diagnosis of LSCT. Their father had PJS but no history of gynecomastia or testicular calcifications. No mutations were found in the tumor suppressor gene LKB1/STK11, which is responsible for about 60% of PJS cases. The genotype of the aromatase cytochrome P450 19, a key enzyme involved in estrogen biosynthesis, was the same in the father and his twins. To reduce gynecomastia and delay skeletal maturation, the children started treatment with anastrozole, an aromatase inhibitor. Growth velocity decreased and gynecomastia diminished. After 2 years of treatment, anastrozole is still currently used at a dosage of 1 mg once daily with no side effects. In this study, a couple of monozygotic twins with PJS, prepubertal gynecomastia and LSCT is reported for the first time and anastrozole appears to be an efficacious medical treatment, as an alternative to orchidectomy, to control the effects of estrogen excess.

Impact of patatin-like phospholipase-3 (rs738409 C>G) polymorphism on fibrosis progression and steatosis in chronic hepatitis C

Only 20% of patients with chronic hepatitis C (CHC) will develop cirrhosis, and fibrosis progression remains highly unpredictable. A recent genome-wide association study identified a genetic variant in the patatin-like phospholipase-3 (PNPLA3) gene (rs738409 C>G) associated with steatosis that was further demonstrated to influence severity of fibrosis in nonalcoholic fatty liver disease. The aim of this study was to assess the impact of this polymorphism on histological liver damage and response to antiviral therapy in CHC. We recruited 537 Caucasian CHC patients from three European centers (Brussels, Belgium [n = 229]; Hannover, Germany [n = 171]; Lyon, France [n = 137]); these patients were centrally genotyped for the PNPLA3 (rs738409 C>G) polymorphism. We studied the influence of rs738409 and other variants in the PNPLA3 region on steatosis and fibrosis assessed both in a cross-sectional and longitudinal manner. Seven other variants previously associated with fibrosis progression were included. Finally, we explored the impact of rs738409 on response to standard antiviral therapy using the interferon lambda 3 (IL28B) [rs12979860 C>T] variant both as a comparator and as a positive control. After adjustment for age, sex, body mass index, alcohol consumption, and diabetes, rs738409 mutant G allele homozygote carriers remained at higher risk for steatosis (odds ratio [OR] 2.55, 95% confidence interval [CI] 1.08-6.03, P = 0.034), fibrosis (OR 3.13, 95% CI 1.50-6.51, P = 0.002), and fibrosis progression (OR 2.64, 95% CI 1.22-5.67, P = 0.013). Conversely, rs738409 was not independently associated with treatment failure (OR 1.07, 95% CI 0.46-2.49, P = 0.875) and did not influence clinical or biological variables.

CONCLUSION

The PNPLA3 (rs738409 C>G) polymorphism favors steatosis and fibrosis progression in CHC. This polymorphism may represent a valuable genetic predictor and a potential therapeutic target in CHC liver damage.

Liver fibrogenesis and genetic factors

Chronic liver diseases lead to the accumulation of fibrosis in the liver with eventual progression to cirrhosis and its complications. However, there is a wide range of inter-individual variation in the liver fibrogenesis process, thus posing a challenge to physicians to identify patients with poor prognosis. As demographic and environmental factors only account for a small portion of fibrogenesis variability, host genetic factors have been suggested as playing an important role. Due to technical limitations, the first genetic studies were restricted to the evaluation of candidate genes having a known or supposed function in liver fibrogenesis. Recently, technological improvements have made it possible to study the whole human genome in a single scan. Genome-wide association studies have considerably heightened the interest in genetics as part of the study of liver fibrogenesis through their identification of previously unsuspected genes that are statistically associated with liver fibrosis. It is thus possible to determine new diagnostic or prognostic genetic markers for the management of patients with chronic liver diseases. Moreover, functional analyses of these genes may provide new insights into the pathophysiology of liver fibrogenesis.

Genetics in liver disease: new concepts

PURPOSE OF REVIEW

Recent advancements in genotyping technology have contributed to an accelerated dissemination of information on sequence variation associated with hepatobiliary diseases and/or quantitative traits.

RECENT FINDINGS

Since the first genome-wide association study (GWAS) on genetic gallstone risk in 2007, a total of more than 25 GWAS related to the field have been reported. The identification of the IL-28B genotype as a critical host factor of natural and treatment-related outcomes in hepatitis C virus infection opens the avenue of personalized medicine and individual risk assessment by genetic information. By contrast, the second recent top-hit variant adiponutrin (PNPLA3) associated with liver fat content and fibrosis progression illustrates the potential of GWAS to identify novel pathobiological pathways. Another emerging research topic is in the designation of genetic markers for specific cirrhosis-related complications, such as spontaneous bacterial peritonitis (NOD2) and hepatic encephalopathy (glutaminase), of potential future relevance in prioritizing patients for preemptive treatment strategies.

SUMMARY

In this article we critically discuss new concepts in the genetics of hepatobiliary diseases with a special focus on the advantages and limitations of the GWAS approach. An update on relevant recent GWAS and selected candidate gene study data will be given.

Genetics and epigenetics in the fibrogenic evolution of chronic liver diseases

Recent years have seen unprecedented progress in the identification and characterization of genetic information related to chronic liver diseases (CLDs). However, despite the conceptual benefit in early recognition of at-risk populations amenable to pre-emptive treatment and/or surveillance strategies, recent genomic research in the field has placed focus on unravelling the genetic architecture of disease susceptibility, while data on genetic markers anticipating an accelerated fibrogenesis in an individual are still limited. Likewise, sequence variation assigning rapid fibrogenic evolution common to CLDs irrespective of etiology are poorly defined aside from PNPLA3 (adiponutrin) as a prominent exception. The emerging field of epigenetics in hepatology has mostly been studied under the perspective of gene regulation, less so as a heritable alteration in gene activity. In this article we will critically discuss recent findings in genomic hepatology with special focus on the (epi)genetic contribution to the fibrogenic evolution of CLDs.

Hepatic insulin resistance in mice with hepatic overexpression of diacylglycerol acyltransferase 2

Mice overexpressing acylCoA:diacylglycerol (DAG) acyltransferase 2 in the liver (Liv-DGAT2) have been shown to have normal hepatic insulin responsiveness despite severe hepatic steatosis and increased hepatic triglyceride, diacylglycerol, and ceramide content, demonstrating a dissociation between hepatic steatosis and hepatic insulin resistance. This led us to reevaluate the role of DAG in causing hepatic insulin resistance in this mouse model of severe hepatic steatosis. Using hyperinsulinemic-euglycemic clamps, we studied insulin action in Liv-DGAT2 mice and their wild-type (WT) littermate controls. Here, we show that Liv-DGAT2 mice manifest severe hepatic insulin resistance as reflected by decreased suppression of endogenous glucose production (0.8 ± 41.8 vs. 87.7 ± 34.3% in WT mice, P < 0.01) during the clamps. Hepatic insulin resistance could be attributed to an almost 12-fold increase in hepatic DAG content (P < 0.01) resulting in a 3.6-fold increase in protein kinase Cε (PKCε) activation (P < 0.01) and a subsequent 52% decrease in insulin-stimulated insulin receptor substrate 2 (IRS-2) tyrosine phosphorylation (P < 0.05), as well as a 64% decrease in fold increase pAkt/Akt ratio from basal conditions (P < 0.01). In contrast, hepatic insulin resistance in these mice was not associated with increased endoplasmic reticulum (ER) stress or inflammation. Importantly, hepatic insulin resistance in Liv-DGAT2 mice was independent of differences in body composition, energy expenditure, or food intake. In conclusion, these findings strengthen the link between hepatic steatosis and hepatic insulin resistance and support the hypothesis that DAG-induced PKCε activation plays a major role in nonalcoholic fatty liver disease (NAFLD)-associated hepatic insulin resistance.

Animal models of nonalcoholic fatty liver disease

In 1980, Ludwig and colleagues described a series of patients with liver histology characterized by the accumulation of fat and the presence of hepatic necroinflammation in the absence of a history of excessive alcohol consumption. They coined the term nonalcoholic steatohepatitis (NASH), which today is regarded as one of the most common causes of liver disease in affluent countries. NASH is a subset of a larger spectrum of diseases termed fatty liver disease (including alcoholic and nonalcoholic fatty liver disease; AFLD and NAFLD, respectively). NAFLD and NASH are linked to visceral adiposity, insulin resistance, dyslipidemia and type 2 diabetes, and are increasing due to the prevalence of the metabolic syndrome. In this context, research has been undertaken using animals to model human steatosis and NAFLD to NASH disease progression. This Review discusses the prevalent dietary and inflammation-based genetic animal models described in recent years.